Reciprocating Fluid Machine

ABSTRACT

A reciprocating fluid machine includes a cylinder block ( 18 ) arranged inside a casing shell ( 16 ) and having cylinder bores ( 38 ), a cylinder head ( 54 ) fastened to the casing shell ( 16 ), a valve plate ( 50 ) interposed between the cylinder block ( 18 ) and the cylinder head ( 54 ) each with a gasket ( 46, 48, 52 ) therebetween, and a fastening device for fastening the valve plate ( 50 ) to the cylinder block ( 18 ). The fastening device includes outer tapped holes ( 42 ) formed in the cylinder block ( 18 ), and outer fastening bolts ( 68 ) extending from the cylinder head side through the valve plate ( 50 ) and the gaskets ( 46, 48, 52 ) and screwed into the respective outer tapped holes ( 42 ). The outer fastening bolts ( 68 ) have axes located outward of a bore distribution circle on which the axes of the cylinder bores ( 38 ) are located, as viewed in the radial direction of the cylinder block ( 54 ), and have bolt heads ( 69 ) located inside the cylinder head ( 54 ).

TECHNICAL FIELD

The present invention relates to reciprocating fluid machines, and moreparticularly, to a reciprocating fluid machine suited for discharging ahigh-pressure working fluid.

BACKGROUND ART

In recent years, development of refrigeration systems is focused on theuse of refrigerants with small global warming potentials inconsideration of global environments. As such refrigerants, natural CO₂(carbon dioxide) gas, for example, has been known.

When CO₂ as a refrigerant passes through a high-pressure section of arefrigeration system, that is, a refrigerant circuit, the CO₂refrigerant turns into a supercritical state. The pressure ofsupercritical CO₂ is approximately seven to ten times higher than thatof a fluorocarbon refrigerant flowing through the high-pressure section.

Accordingly, where CO₂ is used as the refrigerant, a compressor forcirculating the CO₂ refrigerant through the refrigerant circuit isrequired to discharge the high-pressure CO₂ refrigerant. To meet therequirement, the compressor needs to have a discharge chamber with highsealing performance. Patent Documents 1 and 2 identified below, forexample, disclose techniques of sealing the discharge chamber of acompressor.

Patent Document 1: Unexamined Japanese Patent Publication No. 2001-99058Patent Document 2: Unexamined Japanese Patent Publication No. 2002-5014

The compressor disclosed in Patent Document 1 includes a casing, acylinder block arranged inside the casing, and a cylinder head adjoiningthe cylinder block. The cylinder block and the cylinder head arefastened together by a plurality of bolts.

More specifically, a valve plate is sandwiched between the cylinderblock and the cylinder head, with one gasket interposed between thevalve plate and the cylinder block and another gasket interposed betweenthe valve plate and the cylinder head. Thus, the bolts are inserted frominside the casing through the cylinder block, the gasket, the valveplate and the gasket and screwed into the cylinder head. Further, thebolts have their heads sunk into the cylinder block, and the bolt headsare positioned between respective adjacent ones of cylinder bores in thecylinder block, as viewed in the circumferential direction of thecylinder block.

The presence of the bolts makes it difficult to detach the cylinder headfrom the cylinder block when, for example, the top clearance of pistonsin the cylinder bores is to be adjusted. Specifically, the heads of thebolts are located inside the casing, and therefore, prior to removal ofthe bolts, parts such as the pistons and the drive shaft need to bedetached from the cylinder block. Consequently, the use of the boltsleads to lowering in the disassembling efficiency and productivity ofthe compressor.

On the other hand, the compressor disclosed in Patent Document 2includes a center bolt for fixing discharge valves and valve retainersto the valve plate. The center bolt is also used to fasten the valveplate and the cylinder block together.

A center bolt may alternatively be used for fastening the cylinder blockand the cylinder head. In this case, the center bolt is inserted fromoutside of the cylinder head through the cylinder head, the valve plateand the gasket and screwed into the cylinder block.

This center bolt has its head located on the outside of the cylinderhead, and therefore, it is easy to remove the center bolt. However,since the center bolt is positioned substantially at the center of thecylinder head, tightness between the gasket and the valve plate is notuniform over the entire area of the valve plate, making it difficult tosatisfactorily seal the cylinder bores. As a result, the compressionefficiency of the compressor lowers, and especially in cases where theCO₂ refrigerant is used, the compression efficiency remarkably lowers.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a reciprocating fluidmachine which ensures high productivity and high disassemblingefficiency and yet is capable of preventing lowering in compressionefficiency.

To achieve the object, the present invention provides a reciprocatingfluid machine comprising: a housing; a cylinder block having at leastpart thereof contained in the housing and including a plurality ofcylinder bores therein, the cylinder bores having axes located on a boredistribution circle concentric with an axis of the cylinder block; acylinder head fastened to the housing and including a suction chamberand a discharge chamber for a working fluid, the suction and dischargechambers opening toward the cylinder block; a compression unit includinga valve mechanism having pistons received in the respective cylinderbores and capable of reciprocating motion therein and a valve plateinterposed between the cylinder block and the cylinder head each with agasket therebetween, the reciprocating motion of the pistons andoperation of the valve mechanism causing the compression unit tosuccessively carry out suction of the working fluid from the suctionchamber into the cylinder bores, compression of the sucked working fluidin the cylinder bores, and discharge of the compressed working fluidfrom the cylinder bores to the discharge chamber; and a fastening devicefor fastening the valve plate to the cylinder block. The fasteningdevice includes: a plurality of outer tapped holes formed in thecylinder block and extending parallel with the cylinder bores, the outertapped holes having axes located outward of the bore distribution circleas viewed in a radial direction of the cylinder block; and a pluralityof outer fastening bolts extending from a side near the cylinder headthrough the valve plate and the gaskets and screwed into the respectiveouter tapped holes, the outer fastening bolts having bolt heads locatedinside the cylinder head.

In the above reciprocating fluid machine, the valve plate is fastened tothe cylinder block by the multiple outer fastening bolts, and the boltheads of the outer fastening bolts are located inside the cylinder head.In cases where the top clearance of the pistons of the compression unitneeds to be adjusted, it is necessary that the valve plate should bedetached from the cylinder block. Since the bolt heads of the outerfastening bolts are located inside the cylinder head and not inside thehousing, it is possible to access the bolt heads of the outer fasteningbolts from outside of the housing. Accordingly, the outer fasteningbolts, namely, the valve plate can be detached without the need toremove internal parts, such as the drive shaft and the pistons of thecompression unit, from within the housing, thus making it easy to adjustthe top clearance of the pistons. As a result, the time required tomanufacture the fluid machine is shortened, improving the productionefficiency of the fluid machine.

Further, the axes of the outer tapped holes are located outward of thebore distribution circle. Accordingly, the outer fastening bolts screwedinto the outer tapped holes tightly press the gasket at the outerperipheral portion of the valve plate against the cylinder block,thereby significantly improving the sealing performance of the junctionbetween the cylinder block and the valve plate, namely, the sealing ofthe cylinder bores.

Specifically, the bolt heads of the outer fastening bolts are located inthe suction chamber defined in the cylinder head, and the suctionchamber has an annular form surrounding the discharge chamber.

The fastening device may further include: a center tapped hole formed inthe cylinder block coaxially with the cylinder block; and a centerfastening bolt extending from the cylinder head side through the valveplate and the gaskets and screwed into the center tapped hole, thecenter fastening bolt having a bolt head located inside the cylinderhead. In this case, the bolt head of the center fastening bolt islocated in the discharge chamber defined in the cylinder head, and thedischarge chamber is located at the center of the cylinder head.

The center fastening bolt tightly presses the gasket at the centralportion of the valve plate against the cylinder block, whereby thesealing performance of the junction between the cylinder block and thevalve plate is further enhanced.

Preferably, the valve mechanism includes discharge valves forcontrolling discharge of the compressed working fluid, and the centerfastening bolt serves also as a fixing bolt for fixing the dischargevalves to the valve plate.

Further, the fastening device may additionally include: a plurality ofinner tapped holes formed in the cylinder block and having axes locatedinward of the bore distribution circle as viewed in the radial directionof the cylinder block; and a plurality of inner fastening boltsextending from the cylinder head side through the valve plate and thegaskets and screwed into the respective inner tapped holes, the innerfastening bolts having bolt heads located inside the cylinder head. Inthis case, the bolt heads of the inner fastening bolts are located inthe discharge chamber, and the discharge chamber is located at thecenter of the cylinder head.

The inner fastening bolts firmly press the gasket at the central portionof the valve plate against the cylinder block, thereby further improvingthe sealing performance of the junction between the cylinder block andthe valve plate.

The outer fastening bolts may each comprise a stud bolt buried in thecylinder block, and the fastening device may further include nutsscrewed onto the respective stud bolts and pressing the valve plateagainst the cylinder block.

Connecting bolts may be screwed from outside of the cylinder head intothe respective stud bolts, and in this case, the cylinder block and thecylinder head can be fastened together by the connecting bolts.

Preferably, the fluid machine is a compressor used for compressing CO₂refrigerant flowing through a refrigeration circuit. In this case, thecompressor discharges high-pressure CO₂ refrigerant from the cylinderbores into the discharge chamber, but since the sealing performance ofthe junction between the cylinder block and the valve plate is high, theCO₂ refrigerant does not leak to outside from the junction between thecylinder block and the valve plate. Also, the use of CO₂ refrigerantgreatly contributes toward reducing the environment load.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of a compressor, as areciprocating fluid machine, according to a first embodiment of theinvention.

FIG. 2 is a sectional view taken along line II-II in FIG. 1.

FIG. 3 is a front view showing a block-side gasket and a shell-sidegasket, both appearing in FIG. 1.

FIG. 4 is a front view showing a head-side gasket in FIG. 1.

FIG. 5 is a longitudinal sectional view of a compressor, as areciprocating fluid machine, according to a second embodiment of theinvention.

FIG. 6 is a front view showing a shell-side gasket in FIG. 5.

FIG. 7 is a front view showing a block-side gasket in FIG. 5.

FIG. 8 is a front view showing a head-side gasket in FIG. 5.

FIG. 9 is a longitudinal sectional view of a compressor, as areciprocating fluid machine, according to a third embodiment of theinvention.

FIG. 10 is a sectional view taken along line X-X in FIG. 9.

FIG. 11 shows a stud bolt and a nut for fastening a valve plate to acylinder block.

BEST MODE OF CARRYING OUT THE INVENTION

FIG. 1 schematically shows an air-conditioning system for a motorvehicle, or more specifically, part of a refrigeration circuit 2 of thesystem.

The refrigeration circuit 2 includes a circulation path for arefrigerant, and CO₂ gas is used as the refrigerant. A compressor 4 of afirst embodiment as a reciprocating fluid machine, a gas cooler 6, anexpansion valve 8 and an evaporator 10 are inserted in order in thecirculation path. The compressor 4 compresses the refrigerant and thendischarges the compressed, high-pressure refrigerant to the gas cooler6, thereby causing the refrigerant to circulate through therefrigeration circuit 2.

As is clear from FIG. 1, the compressor 4 is of a swash plate type, andthis type of compressor is capable of varying its displacement.

The compressor 4 has a housing including a front casing 12. The frontcasing 12 is in the form of a stepped cylinder and has a boss 14 and acasing shell 16. The boss 14 is located at one end of the front casing12 and has a diameter smaller than that of the casing shell 16.

A cylinder block 18 is fitted into the casing shell 16 and has asubstantially cylindrical shape. The cylinder block 18 defines a crankchamber 20 inside the casing shell 16 and has one end face facing thecrank chamber 20 and the other end face exposed from the casing shell16.

The cylinder block 18 has, for example, seven cylinder bores 36. Thecylinder bores 36 extend through the cylinder block 18 in parallel withthe axis of the block 18. As is clear from FIG. 2, the cylinder bores 36have their axes located on a bore distribution circle concentric withthe axis of a drive shaft 24 and are arranged at equal intervals in thecircumferential direction of the cylinder block 18.

A compression unit is arranged inside the front casing 12. The followingexplains the compression unit.

The compression unit includes the drive shaft 24, which is arrangedcoaxially with the cylinder block 18. The drive shaft 24 extends throughthe crank chamber 20 and is rotatably supported by both of the frontcasing 12 and the cylinder block 18 through bearings 26 and 28,respectively. A swash plate 30 is mounted on the drive shaft 24 througha tilt mechanism 32 and accommodated in the crank chamber 20. The tiltmechanism 32 includes a rotor 34 rotated together with the drive shaft24 and causes the swash plate 30 to rotate together with the drive shaft24 through the rotor 34 while at the same time permits the swash plate30 to tilt relative to the drive shaft 24.

The drive shaft 24 has one end portion 25 projecting from the casingshell 16 into the boss 14, and a mechanical seal 74 is arranged betweenthe end portion 25 and the casing shell 16. The mechanical seal 74 sealsthe crank chamber 20 in a gastight fashion.

An electromagnetic clutch 76 is coupled to the end portion 25 of thedrive shaft 24 and includes a pulley 78. The pulley 78 is rotatablysupported on the outer peripheral surface of the boss 14 through abearing 80. The pulley 78 is connected to a driving source, such as anengine or a motor, and is rotated in one direction by motive powersupplied from the driving source. Further, the pulley 78 has a solenoid82 received therein, and the solenoid 82 is fixed to the casing shell16.

When the solenoid 82 is energized, the electromagnetic clutch 76transmits rotation of the pulley 78 to the drive shaft 24. On the otherhand, when the solenoid 82 is de-energized, the electromagnetic clutch76 stops transmitting rotation of the pulley 78 to the drive shaft 24.

The casing shell 16 has a plurality of mounts 84 formed integrally on anouter peripheral surface thereof. The mounts 84 each have a boltinsertion hole therein and are used to install the compressor 4 in anengine compartment.

A piston 38 is received in each cylinder bore 36 and includes a tail 39projecting into the crank chamber 20. The tail 39 is in the form of theletter U and opens in the radial direction of the cylinder bock 18toward the drive shaft 24 as well as in the circumferential direction ofthe cylinder block 18. Also, each tail 39 has a spherical seat thereinfor slidably supporting a pair of shoes 44. The shoes 44 aresemispherical in shape and hold the outer peripheral edge of the swashplate 30 therebetween. Thus, while the swash plate 30 is rotating, theouter peripheral edge thereof and the shoes 44 are kept in slidingcontact with each other.

The cylinder block 18 has a center tapped hole 40 formed in the otherend face thereof. The center tapped hole 40 is located on the axis ofthe cylinder block 18 and extends parallel with the cylinder bores 36.

Further, seven outer tapped holes 42 are formed in the other end face ofthe cylinder block 18. The outer tapped holes 42 have their axes locatedoutward of the aforementioned bore distribution circle, as viewed in theradial direction of the cylinder block 18, and are arranged at equalintervals in the circumferential direction of the cylinder block 18.More specifically, the axes of the outer tapped holes 42 are located ona hole distribution circle having a larger diameter than the boredistribution circle, and the outer tapped holes 42 are individuallypositioned between adjacent ones of the cylinder bores 36 as viewed inthe circumferential direction of the cylinder block 18.

As is clear from FIG. 1, the other end face of the cylinder block 18 isflush with the counterpart of the casing shell 16, and a cylinder head54 adjoins the other end faces with a valve plate 50 therebetween.

A block-side gasket 46 is interposed between the other end face of thecylinder block 18 and the valve plate 50, and a shell-side gasket 48 isinterposed between the other end face of the casing shell 16 and thevalve plate 50. Further, a head-side gasket 52 is sandwiched between thevalve plate 50 and the cylinder head 54. The gaskets 46, 48 and 52respectively serve as a seal between the cylinder block 18 and the valveplate 50, a seal between the casing shell 16 and the valve plate 50, anda seal between the valve plate 50 and the cylinder head 54.

Ten tapped holes 17, for example, are formed in the other end face ofthe casing shell 16. The tapped holes 17 extend in the axial directionof the casing shell 16 and are arranged at equal intervals in thecircumferential direction of the casing shell 16. The valve plate 50 andthe cylinder head 54 have ten through holes 53 and 55, respectively,formed through their outer peripheral portions and aligned with therespective tapped holes 17. Connecting bolts 56 are inserted fromoutside of the cylinder head 54 into the respective through holes 53 and55 and are screwed into the respective tapped holes 17. The connectingbolts 56 separably fix the cylinder head 54 to the casing shell 16 withthe valve plate 50 and the gaskets 48 and 52 therebetween.

Further, the valve plate 50 has through holes 51 aligned with therespective outer tapped holes 42 of the cylinder block 18. Outerfastening bolts 68 are inserted into the respective through holes 51 andscrewed into the respective tapped holes 42. Namely, the outer fasteningbolts 68 fasten the valve plate 50 to the cylinder block 18 togetherwith the gaskets 46 and 52.

The cylinder head 54 has a suction chamber 58 and a discharge chamber 60defined therein, and the suction and discharge chambers 58 and 60individually open in the end face of the cylinder head 54 adjacent tothe valve plate 50. Namely, the suction and discharge chambers 58 and 60open toward the cylinder block 54. As is clear from FIG. 1, thedischarge chamber 60 is located at the center of the cylinder head 54,and the suction chamber 58 is an annular chamber surrounding thedischarge chamber 60. The outer fastening bolts 68 have their bolt heads69 located in the suction chamber 58.

A suction port and a discharge port (neither of which is shown)communicating with the suction and discharge chambers 58 and 60,respectively, are formed in the outer peripheral wall of the cylinderhead 54. The suction and discharge ports are connected to theaforementioned refrigerant circulation path.

A pressure regulation passage (not shown) for connecting the dischargechamber 60 and the crank chamber 20 is formed through the cylinder block18 and the valve plate 50. Also, an orifice passage connecting thesuction chamber 58 and the crank chamber 20 at all times is formedthrough the cylinder block 18 and the valve plate 50. In FIG. 1, only afixed orifice 62 formed in the valve plate 50 is shown as part of theorifice passage.

The cylinder head 54 further includes a solenoid control valve (notshown) accommodated therein. In this embodiment, the solenoid controlvalve has a valve element for opening and closing the pressureregulation passage, a solenoid, and a pressure-sensitive actuatorapplied with the pressure in the suction chamber 58. The solenoid andthe pressure-sensitive actuator cooperate with each other to actuate thevalve element, thereby adjusting the opening of the pressure regulationpassage and, as a consequence, controlling the pressure in the crankchamber 20.

The solenoid control valve may be of the type including nopressure-sensitive actuator. In this case, the valve element is actuatedby the solenoid of the solenoid control valve, whereby the opening ofthe pressure regulation passage, that is, the pressure in the crankchamber 20 is controlled.

The valve plate 50 is an element constituting a valve mechanism. Thevalve mechanism includes suction and discharge holes 58 a and 60 aassociated with each of the cylinder bores 36 and formed through thevalve plate 50. The suction holes 58 a communicate with the suctionchamber 58, and the discharge holes 60 a communicate with the dischargechamber 60. Each suction hole 58 a can be opened and closed by a suctionvalve (not shown). The suction valve comprises a reed valve and isinterposed between the other end face of the cylinder block 18 and thevalve plate 50. On the other hand, the discharge holes 60 a can beopened and closed by a discharge valve unit 66. The discharge valve unit66 includes reed valves 61 (see FIG. 2) arranged on the surface of thevalve plate 50 facing the discharge chamber 60, and valve retainers 63.The reed valves 61 and the valve retainers 63 are fixed by a centerfastening bolt 64 to the cylinder block 18 with the valve plate 50therebetween. Specifically, the center fastening bolt 64 extends throughthe valve plate 50 and the gaskets 46 and 52 and is screwed into theaforementioned center tapped hole 40 of the cylinder block 18. The bolthead of the center fastening bolt 64 is located in the discharge chamber60.

As is clear from FIG. 2, the reed valves 61 and the valve retainers 63have a star-like shape corresponding to the arrangement of the dischargeholes 60 a. The suction valves also have a star-like shape correspondingto the arrangement of the suction holes 58 a.

FIG. 3 shows in detail the block-side gasket 46 and the shell-sidegasket 48, both mentioned above.

The block-side gasket 46 has a circular shape coinciding with the otherend face of the cylinder block 18 and has a hole 40H at its centerthrough which the center fastening bolt 64 is passed. Also, a pluralityof holes 42H are formed in the outer peripheral portion of theblock-side gasket 46 to allow the respective outer fastening bolts 68 tobe passed therethrough.

The shell-side gasket 48 functions also as an adjusting member foradjusting the top clearance of the pistons 38, as described later.Accordingly, the shell-side gasket 48 is prepared separately from theblock-side gasket 46. The shell-side gasket 48 has a plurality of holes17H through which the respective connecting bolts 56 are passed. As isclear from FIG. 3, the shell-side gasket 48 has an outward formcoinciding with the contour of the casing shell 16.

FIG. 4 shows the head-side gasket 52.

The head-side gasket 52 has an outward form coinciding with the contourof the cylinder head 54, and has an aperture 52 a formed at its centerand permitting the discharge valve unit 66 to be arranged, a pluralityof holes 42 h through which the respective outer fastening bolts 68 arepassed, and a plurality of holes 55 h through which the respectiveconnecting bolts 56 are passed.

In the first embodiment described above, the valve plate 50 is not onlyfastened to the cylinder block 18 by the center fastening bolt 64 withthe gasket 46 therebetween but also is clamped between the cylinderblock 18 and the cylinder head 54 by the connecting bolts 56 and theouter fastening bolts 68 together with the gaskets 46, 48 and 52.

When the solenoid of the electromagnetic clutch 76 is energized, thatis, when the clutch 76 is in operation, the electromagnetic clutch 76transmits the motive power from the driving source to the drive shaft24, so that the drive shaft 24 rotates in one direction. The rotation ofthe drive shaft 24 is converted through the swash plate 30 toreciprocating motion of the individual pistons 38. As each piston 38reciprocates, the refrigerant undergoes a series of processes includinga suction process in which the refrigerant is sucked from the suctionchamber 58 into the pressure chamber of the cylinder bore 36 through thesuction valve, a compression process in which the sucked refrigerant iscompressed in the pressure chamber, and a discharge process in which thecompressed refrigerant is discharged through the discharge valve 61 tothe discharge chamber 60.

The amount of the refrigerant discharged, or the displacement, isdetermined by the tilt angle of the swash plate 30, namely, the lengthof the reciprocating stroke of the piston 38. The tilt angle of theswash plate 30 is adjusted by controlling the pressure in the crankchamber 20 by means of the aforementioned solenoid control valve.

Generally, the compressor 4 is assembled in the manner described below.

First, the cylinder block 18 is fixed on a workbench (not shown) bymaking use of the outer fastening bolts 68. The outer fastening bolts 68are passed through the workbench and screwed into the respective outertapped holes 42 of the cylinder block 18.

Then, with internal parts such as the swash plate 30, the tilt mechanism32, the pistons 38 and the shoes 44 fitted onto the drive shaft 24, thedrive shaft 24 is rotatably supported on the cylinder block 18 throughthe bearing 28 while at the same time the pistons 38 are inserted intothe respective cylinder bores 36 of the cylinder block 18. Subsequently,the front casing 12 is fitted over the cylinder block 18. Thus, thedrive shaft 24 is rotatably supported by the front casing 12 through thebearing 26 with the internal parts located inside the front casing 12,and the end portion of the drive shaft projects from the front casing12.

At this stage, a dimension by which the top clearance of the pistons 38needs to be adjusted is measured, and a shell-side gasket 48 with athickness corresponding to the measured dimension is selected.

Subsequently, with the internal parts contained in the front housing 12,the outer fastening bolts 68 are removed from the cylinder block 18, sothat the cylinder block 18 is separated from the workbench. Theblock-side gasket 46 and the shell-side gasket 48 selected in theaforementioned manner are then placed between the cylinder block 18 andthe valve plate 50, and the valve plate 50 is fastened to the frontcasing 12 and the cylinder block 18 by the outer fastening bolts 68 withthe block-side gasket 46 and the shell-side gasket 48 therebetween. Atthis time, the discharge valve unit 66 is fixed, together with the valveplate 50, to the cylinder block 18 by the center fastening bolt 64.

Then, the cylinder head 54 containing the aforementioned solenoidcontrol valve is abutted against the valve plate 50 with the head-sidegasket 52 therebetween and is fastened to the front housing 12 by theconnecting bolts 56.

Finally, the electromagnetic clutch 76 is coupled to the end portion 25of the drive shaft 24 projecting into the boss 14 of the front housing12, thus completing the assembling of the compressor 4.

The present invention is not limited to the compressor of the firstembodiment explained above and may be modified in various ways. Thefollowing describes compressors according to second and thirdembodiments. In the following description of the second and thirdembodiments, identical reference numerals are used to denote elementsand parts having the same functions as those of the first embodiment,and description of such elements and parts is omitted.

FIGS. 5 through 8 illustrate the compressor according to the secondembodiment.

As is clear from FIG. 5, a cylinder block 18A forms part of a fronthousing 12A. Specifically, the cylinder block 18A is in the form of astepped cylinder and has a flange 19 interposed between a casing shell16A and the cylinder head 54. In this arrangement, a shell-side gasket48A is sandwiched between the flange 19 of the cylinder block 18A andthe other end face of the casing shell 16A. The shell-side gasket 48A isshown in detail in FIG. 6.

The flange 19 has through holes 19 a for passing the connecting bolts 56therethrough, and thus, the connecting bolts 56 are screwed into thecasing shell 16A through the cylinder block 18A.

In the second embodiment, a valve plate 50A is in the form of a circlewith an outer diameter equal to the inner diameter of the flange 19. Thecylinder head 54 has a circular recess 54 a for receiving the valveplate 50A. Thus, as is clear from FIG. 5, the connecting bolts 56 do notpenetrate through the valve plate 50A but extend outward of the valveplate 50A.

The discharge valve unit 66 is fixed to the valve plate 50A by a bolt 73a and a nut 73 b.

In the second embodiment, a block-side gasket 46A between the cylinderblock 18A and the valve plate 50A is also held between the cylinderblock 18A and the cylinder head 54. The block-side gasket 46A alsofunctions as the adjusting member for adjusting the top clearance of thepistons 38. A head-side gasket 52A is interposed between the valve plate50A and the cylinder head 54.

FIG. 7 shows the block-side gasket 46A in detail. As clearly shown inFIG. 7, the block-side gasket 46A has a plurality of holes 17H′ forpassing the respective connecting bolts 56 therethrough.

FIG. 8 illustrates the head-side gasket 52A in detail. As is clear fromFIG. 8, the head-side gasket 52A does not have the holes 55 h for theconnecting bolts 56, as distinct from the head-side gasket 52 shown inFIG. 4.

Also in the second embodiment, the valve plate 50A is held between thecylinder block 18A and the cylinder head 54 by means of the connectingbolts 56 and the outer fastening bolts 68 together with the block-sidegasket 46A and the head-side gasket 52A.

On assembly of the compressor 4A shown in FIG. 5, the outer fasteningbolts 68 extend from the cylinder head side through the valve plate 50Aand are screwed into the respective outer tapped holes 42 in thecylinder block 18A.

FIGS. 9 and 10 illustrate the compressor according to the thirdembodiment.

In the compressor 4B of FIG. 9, a cylinder block 18B additionallyincludes seven inner tapped holes 70. The inner tapped holes 70 havetheir axes located on a hole distribution circle having a diametersmaller than that of the hole distribution circle on which the outertapped holes 42 are distributed, and are arranged at equal intervals inthe circumferential direction of the cylinder block 18B. Needless tosay, the inner tapped holes 70 also are individually arranged betweenadjacent ones of the cylinder bores 38 as viewed in the circumferentialdirection of the cylinder block 18B.

A block-side gasket 46B is interposed between the cylinder block 18B anda valve plate 50B, and the valve plate 50B and the block-side gasket 46Beach have holes coinciding with the respective inner tapped holes 70.Thus, inner fastening bolts 71 are inserted through these holes andscrewed into the respective inner tapped holes 70. The inner fasteningbolts 71 fasten the valve plate 50B to the cylinder block 18B togetherwith the block-side gasket 46B and have bolt heads 72 located in thedischarge chamber 60.

The arrangement of the inner fastening bolts 71 and of the outerfastening bolts 68 is clearly shown in FIG. 10.

In the compressors of the first to third embodiments, the bolt heads 69of the outer fastening bolts 68 are not exposed to the crank chamber 20but are located in the suction chamber 58. Namely, the outer fasteningbolts 68 are screwed into the respective outer tapped holes 42 of thecylinder block 18 (18A, 18B) from the same side as the cylinder head 54.

With the compressor of the present invention, therefore, the topclearance of the pistons can be adjusted with ease, unlike thecompressor disclosed in the aforementioned Patent Document 1.Specifically, to adjust the top clearance, the gasket needs to bereplaced, that is, the valve plate needs to be detached. In the case ofthe compressor disclosed in Patent Document 1, the internal parts suchas the pistons and the drive shaft need to be removed from the fronthousing 12 before the valve plate is detached (the bolts are removed),as mentioned above. Then, after a suitable gasket 48 (48A) for adjustingthe top clearance is selected, the internal parts need to be againfitted in the front housing 12. Consequently, in the case of thecompressor of Patent Document 1, not only the manufacturing timerequired per compressor increases but also complicated management isneeded during the disassembling and reassembling of the compressor, inorder to avoid damage to the internal parts.

In the compressor of the present invention, by contrast, the outerfastening bolts 68 can be unscrewed on the same side as the cylinderhead 54, thus making it possible to detach the valve plate 50 (50A,50B), that is, to adjust the top clearance without the need to removethe internal parts from the cylinder block 18 (18A, 18B). Consequently,the compressor 4 (4A, 4B) can be easily assembled, whereby theproduction efficiency is significantly improved and also damage to theinternal parts can be avoided.

Further, since the outer fastening bolts 68 are located in the outerperipheral portion of the valve plate 50 (50A, 50B), the block-sidegasket 46 (46A, 46B) is tightly pressed against the other end face ofthe cylinder block 18 (18A, 18B) by the outer fastening bolts 68 so thatthe block-side gasket may be in close contact with the surface aroundthe cylinder bores 36. The sealing performance of the junction betweenthe cylinder block 18 and the valve plate 50 (50A, 50B) thereforegreatly improves, and even in cases where CO₂ gas is used as therefrigerant, the compression efficiency of the compressor does notlower.

In the first embodiment, the center fastening bolt 64 also fastens thevalve plate 50 to the cylinder block 18. Accordingly, the centralportion of the valve plate 50 also is brought into close contact withthe other end face of the cylinder block 18 through the block-sidegasket 46, thus further improving the sealing performance of thejunction between the cylinder block 18 and the valve plate 50.

Moreover, where the inner fastening bolts 71 are additionally used as inthe third embodiment, the sealing performance of the junction betweenthe cylinder block 18 and the valve plate 50 can be remarkably improved.

The present invention is not limited to the first to third embodimentsdescribed above and may be modified in various ways without departingfrom the scope of the invention.

For example, the outer fastening bolts 68 and the inner fastening bolts71 may each be replaced by a stud bolt 100 shown in FIG. 11. The studbolt 100 is buried in the cylinder block 18, and the valve plate 50 isfastened to the cylinder block 18 by a nut 102 screwed onto the studbolt 100.

Further, a connecting bolt 104 may be screwed from outside of thecylinder head 54 into the stud bolt 100, as indicated by thedot-dot-dash line in FIG. 11. In this case, the cylinder head 54 and thecylinder block 18 can be fastened by the connecting bolts 104.

The reciprocating fluid machine to which the present invention isapplied may alternatively be a fixed-displacement compressor orexpander.

1. A reciprocating fluid machine comprising: a housing; a cylinder blockhaving at least part thereof contained in the housing and including aplurality of cylinder bores therein, the cylinder bores having axeslocated on a bore distribution circle concentric with an axis of thecylinder block; a cylinder head fastened to the housing and including asuction chamber and a discharge chamber for a working fluid, the suctionand discharge chambers opening toward the cylinder block; a compressionunit including a valve mechanism having pistons received in therespective cylinder bores and capable of reciprocating motion thereinand a valve plate interposed between the cylinder block and the cylinderhead each with a gasket therebetween, the reciprocating motion of thepistons and operation of the valve mechanism causing the compressionunit to successively carry out suction of the working fluid from thesuction chamber into the cylinder bores, compression of the suckedworking fluid in the cylinder bores, and discharge of the compressedworking fluid from the cylinder bores to the discharge chamber; and afastening device for fastening the valve plate to the cylinder block,the fastening device including a plurality of outer tapped holes formedin the cylinder block and extending parallel with the cylinder bores,the outer tapped holes having axes located outward of the boredistribution circle as viewed in a radial direction of the cylinderblock, and a plurality of outer fastening bolts extending from a sidenear the cylinder head through the valve plate and the gaskets andscrewed into the respective outer tapped holes, the outer fasteningbolts having bolt heads located inside the cylinder head.
 2. Thereciprocating fluid machine according to claim 1, wherein the bolt headsof the outer fastening bolts are located in the suction chamber, and thesuction chamber has an annular form surrounding the discharge chamber.3. The reciprocating fluid machine according to claim 1, wherein thefastening device further includes: a center tapped hole formed in thecylinder block coaxially with the cylinder block; and a center fasteningbolt extending from the side near the cylinder head through the valveplate and the gaskets and screwed into the center tapped hole, thecenter fastening bolt having a bolt head located inside the cylinderhead.
 4. The reciprocating fluid machine according to claim 3, whereinthe bolt head of the center fastening bolt is located in the dischargechamber, and the discharge chamber is located at center of the cylinderhead.
 5. The reciprocating fluid machine according to claim 4, whereinthe valve mechanism includes discharge valves for controlling dischargeof the compressed working fluid, and the center fastening bolt servesalso as a fixing bolt for fixing the discharge valves to the valveplate.
 6. The reciprocating fluid machine according to claim 1, whereinthe fastening device further includes: a plurality of inner tapped holesformed in the cylinder block and having axes located inward of the boredistribution circle as viewed in the radial direction of the cylinderblock, and a plurality of inner fastening bolts extending from the sidenear the cylinder head through the valve plate and the gaskets andscrewed into the respective inner tapped holes, the inner fasteningbolts having bolt heads located inside the cylinder head.
 7. Thereciprocating fluid machine according to claim 6, wherein the bolt headsof the inner fastening bolts are located in the discharge chamber, andthe discharge chamber is located at center of the cylinder head.
 8. Thereciprocating fluid machine according to claim 1, wherein the outerfastening bolts each comprise a stud bolt buried in the cylinder block,and the fastening device further includes nuts screwed onto therespective stud bolts and pressing the valve plate against the cylinderblock.
 9. The reciprocating fluid machine according to claim 1, whereinthe fluid machine is a compressor used for compressing CO₂ refrigerantflowing through a refrigeration circuit.